1. Field of the Invention
The present invention relates to a method of manufacturing a plastic article having micro-openings defined therein by working a semi-finished plastic structure having microrecesses defined in one side thereof ranging from about two to about several hundred micrometers in size. The end product is a plastic article provided with micro-openings, such as a grid-shaped, mesh-like microstructured article of plastic.
2. Description of the Related Art
The term "microrecesses" as used herein is understood to mean negative structures defined in a semi-finished plastic structure or product that have dimensions which lie in a range between two micrometers and several hundred micrometers.
The method according to the invention is based on semi-finished plastic structures having opposing sides of preferably a plate-like shape in which microrecesses, which determine the shape of the micro-openings defined in the end product, are pre-shaped on one side. Such semi-finished structures may be obtained, for example, if metal tools, produced with the aid of mechanical microprocesses--for example, by working them with a shaping diamond or by X-ray deep-etch lithography--are copied in plastic. A plastic, such as polymethyl methacrylate (PMMA), is usually used for the copying. In the prior art copying methods of injection molding or reaction casting, the process itself requires that a relatively thick base plate is formed underneath the microstructures.
Federal Republic of Germany Patent No. 3,842,610 C1, which corresponds to U.S. Pat. No. 5,055,163 which is incorporated herein by reference, discloses the production of metal foils or plates that have a plurality of fine openings or slits. In this process, a tool is produced that is provided with microstructures on its surface. The microstructures of the tool are copied by means of a molding substance composed of an electrically conductive layer and an electrically insulating layer. The microstructures of the tool are defined through the electrically insulating layer into the electrically conductive layer to produce a mold. The mold is then filled with a metal by electroplating using the electrically conductive layer as the cathode and, finally, the molding substance is removed.
If the tool has microstructures to be copied that are of the type that taper toward the electrically conductive layer, the size of the fine openings in the foils or plates can be set by filling the molding substance to a corresponding depth by electroplating. This process, however, produces only microstructured bodies made of metal.
Federal Republic of Germany Patent No. 3,813,711 A1, which corresponds to U.S. Pat. No. 4,862,575 which is incorporated herein by reference, discloses a method of finishing the surface of an object that is provided with grooves. The method includes the steps of filling grooves in the grooved surface with a softened, brittle material and subsequently milling out the grooved surface.
The brittle material may be a water soluble material, such as, for example, starch, dextrin, a sucrose compound, a carbonate or a chloride. However, a sublimable material, particularly naphthalene, is also suitable as the brittle material. The method is employed on metal surfaces.
The water soluble materials employed as powders to fill the grooves, however, do not permit complete filling of the spaces between the microstructures. Cavities remain because the grain size of conventional powders lies in a range on the order of magnitude of the microstructures. The use of substances which sublimate, on the other hand, requires temperatures above 80.degree. C. at which temperatures sensitive microstructures, for example, those made of PMMA, may deform. The publication, moreover, provides no teaching or suggestion as to how the above-described end products can be obtained.
Japanese Laid-Open Application No. 63-11,244 discloses a method by which burr-free holes can be drilled into work-pieces that are closed on one side. For this purpose, the workpiece that is closed on one side, is filled with polyurethane resin at about 150.degree. C., and is drilled after the resin hardens. The polyurethane resin is then removed by washing with water. Because of the poor solubility of hardened polyurethane resin in water, however, this can obviously not be effected in a gentle manner that would be compatible with the production of microstructures. The working of microstructured, semi-finished plastic products is not discussed.
German Democratic Republic Patent No. 0,282,410 A5 discloses a method of deburring perforated components, particularly sieves, which are straight or rounded into cylinders. The holes of the perforated component are filled with a smoothable, hardenable substance before being machined, which can be easily removed after machining. A polyurethane casting substance or gypsum is employed as the hardenable substance. The removal of this substance is mechanical, for example, by pressurized water, or chemical, for example, by heated hydrochloric acid. The process is therefore unsuitable for microstructured bodies made of plastic.
Federal Republic of Germany Published Application No. 2,812,719 discloses a method for machining porous workpieces in which the pores of the material are filled before machining with a substance that supports the sides of the pore walls and thus seals the pores by lateral pressure. Burr formation is thus made more difficult or is prevented entirely. The type of the filler, its removal, and the manner of working, however, are not disclosed by the reference.
Federal Republic of Germany Published Application No. 3,811,748 C2 discloses a method of producing microgratings, microscreens, etc. in which a plate-shaped body is microstructured on both sides. During working, a foil-like supporting layer is releasably glued to the plate-shaped body. The body is held on a vacuum tensioning device by way of the supporting layer. After the body has been worked, the supporting layer, as well as the adhesive--which is not specified in detail--must be removed.
It is thus an object of the present invention to produce articles having micro-openings, for example, microgratings or micromeshes which, in contrast to the above-mentioned Federal Republic of Germany Patent No. 3,842,610 C1 are not composed of metal but of plastic and which, similar to the process disclosed in that publication, have a size for the openings in the end product which is settable to the desired value in one process step performed, in the case of the present invention, on a semi-finished plastic structure that has defined therein specially pre-shaped microrecesses.
It is another object of the present invention to provide a manufacturing method for plastic articles having micro-openings defined therein which is to be implemented in such a way that a semi-finished plastic structure can be positioned and held during working on a vacuum tensioning device even though the plastic article end product constitutes a microstructured body that is provided with openings, for example, a grating type body.
It is yet another object of the present invention to provide a manufacturing method which may be implemented without deforming or damaging the filigree-like structures of the semi-finished plastic structure.